Mapping Mountains – Hill Reclassifications – 200m Twmpau

Rhos Swydd (SO 117 650) – 200m Sub-Twmpau addition

There has been confirmation of an addition to the list of 200m Twmpau, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Rhos Swydd (SO 117 650)

The criteria for the list that this addition applies to are:

200m Twmpau – Welsh hills at or above 200m and below 300m in height that have 30m minimum drop, with an accompanying sub list entitled the 200m Sub-Twmpau, with the criteria for this sub category being all Welsh hills at or above 200m and below 300m in height with 20m or more and below 30m of drop.  The list is authored by Myrddyn Phillips, with the word Twmpau being an acronym standing for thirty welsh metre prominences and upward. 

200m Twmpau by Myrddyn Phillips

The name the hill is now listed by is Rhos Swydd, and this was derived from the Ordnance Survey series of Six-Inch maps, and it is adjoined to the Fforest Glud group of hills, which are situated in the eastern part of South Wales (Region B, Sub-Region B3), and it is positioned with a minor road to its north-west, the A44 road to its south-west and the A488 road to its south-east, and has the town of Llandrindod towards the south-west.

When the original 200m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was not included in the accompanying Hills to be surveyed sub list, as it was considered not to meet the criteria then used for this sub category.

After the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-evaluated and it was listed with an estimated c 20m of drop, based on an estimated c 267m summit height and an estimated c 247m bwlch height, with both heights based on interpolation of 10m contouring that appears on the Ordnance Survey 1:25,000 Explorer map. 

Extract from the Ordnance Survey 1:25,000 Explorer map

However, it was not until LIDAR became available that the details for this hill could be accurately re-assessed.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales.

Therefore, the confirmation of the addition of this hill to 200m Sub-Twmpau status is due to LIDAR analysis, resulting in a 268.0m summit height and a 244.8m bwlch height, with these values giving this hill 23.2m of drop, which is sufficient for it to be classified as a 200m Sub-Twmpau. 

 

The full details for the hill are: 

Group:  Fforest Glud 

Name:  Rhos Swydd 

OS 1:50,000 map:  148

Summit Height:  268.0m (LIDAR) 

Summit Grid Reference:  SO 11706 65038 (LIDAR) 

Bwlch Height:  244.8m (LIDAR) 

Bwlch Grid Reference:  SO 12253 65143 (LIDAR) 

Drop:  23.2m (LIDAR) 

 

Myrddyn Phillips (April 2026)